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Home , Agriculture, Crop, Intercropping

doi:10.2489/jswc.64.2.55A Conservation Does have a role in In Practice modern ? Stephen Machado

ntercropping—growing two or more at the same time on a single I —is an ancient practice still used in much of the developing world. For example, in , corn ( mays L.), (Sorghum bicolor (L.) Moench), or (Panicum and Pennisetum spp.) are grown with pumpkin (Cucurbita spp.) (Vigna unguiculata (L.) Walp), pigeon (Cajanus cajan (L.) Millsp.), or (Phaseolus spp.). Cocoa ( L.) is grown with yams ( spp.) or (Manihot esculenta Crantz). In the tropical , (corn) is grown with beans and squash (Cucurbita spp.). In both Africa and Latin America, beans or peas (Pisum sativum L.) climb tall cornstalks while pumpkins or squash cover the ground below. In these coun- - intercrop at the Columbia Basin Agricultural Research Center, Oregon tries, many have limited access to University, Moro, Oregon. agricultural chemicals and equipment so prevalent in the developed world. Besides, varieties were developed and fertilized to tinue to increase, while their manufacture intercropping is much less risky in that if bring about the that contributes to gas emissions. one fails another or the others may could feed rapidly growing populations. Also, the lack of diversity in still be harvested. Global use increased from 24.5 fosters problems, as well as increased Before the 1940s in the million Mg (27 million tn) in the late pressure. The latter problem is partly and Europe, growing more than one crop 1950s to 210.5 million Mg (197 million because of monoculture’s less diverse insect in the same field was common practice tn) in 2007–2008, according to and community that includes fewer or no pest (Kass 1978; Andersen 2005), again because Agricultural Organization data. Of this predators (Horwith 1985; Horrigan et al. there was less risk. But with mechaniza- composite fertilizer mix, 65% was nitro- 2002). In addition, potent that tion and the availability of relatively cheap gen, 19%, , and 16% . kill both pests and their natural enemies synthetic and , mono- And worldwide demand for fertilizer is still are currently being used. US synthetic cropping—i.e., growing only one crop in rising, albeit at a slower rate due to a some- use increased 33-fold since a field at a time—became the economi- what increased nutrient use efficiency. 1945, but despite this substantial pesticide cally efficient way to go (Horwith 1985). But now, fertilizer shortages are cost and use, crop yields continue to be No longer was it necessary to grow a developing and costs are escalating. The threatened by , , and disease. with a to provide nutrients composite fertilizer price increased 113% Reasons include built-up pesticide resis- needed by the latter. Under monocrop- between 2000 and 2007, led by gains in tance, outbreaks of secondary pests, and ping, synthetic fertilizer-intensive regime, prices (Huang 2007). The US susceptibility in the (Brenner 1991). crop yields increased dramatically. US corn price of increased from $250 As these and other problems with mono- yields increased from 1.9 Mg ha–1 (30 bu Mg–1 ($227 tn–1) in 2000 to $474.4 Mg–1 farming become more apparent, ac–1) in the 1940s to 9.7 Mg ha–1 (154 bu ($523 tn–1) in 2007, while urea (the main “” is becoming a household ac–1) in 2008. As were developed solid US fertilizer form) changed from word, and interest in intercropping is for various single cash crops, intercropping $181.4 Mg–1 ($200 tn–1) to $410.9 Mg–1 growing as, possibly, part of the solution. became impractical. These new modern ($453 tn–1) (Huang 2007). Meanwhile, Already double cropping is being widely farming methods were also spread to parts environmental problems associated with practiced as an alternative to monoculture. of the developing world as high-yielding heavy fertilizer use are becoming well In the Midwest, are being rotated known—e.g., surface- and with corn. While itself is a valu- Stephen Machado is an agronomist at the pollution, acidification, and ammonia able crop, it fixes nitrogen for the next Columbia Basin Agricultural Research Center, Oregon State University, Pendleton, Oregon. volatilization. And as synthetic fertilizer is a year’s corn crop. Similarly, across the nation petroleum-based product, prices will con- and beyond, grain crops are rotated with

PROOF * NOT FOR DISTRIBUTION journal of soil and conservation March/April 2009—vol. 64, no. 2 55A a legume, which may itself be a crop or it alters the quality of the other crop, mak- wheat farmers. That is, seeking to maxi- may be grown as a . However, in ing it a less attractive host for a predator or mize yield, these farmers figure the amount dryland regions of the , a parasite. For example, onions (Allium cepa of nitrogen to apply to meet the target most grain farmers prefer to stick with L.) are planted with carrots ( yield. Generally, as is it certainly more grain, not being willing to give up their L.) as they mask the carrot smell for carrot convenient, they apply the precise amount for a year of legume without flies (Sullivan 2003). The trap hypothesis is before the crop is planted or at planting. good ways to market that crop. that one crop attracts pests that would oth- Ideally, they should apply some fertilizer at Intercropping has four general subcat- erwise have gone to what is being grown planting and then apply the remainder as egories. There is mixed intercropping, no as the principal crop. For weeds, a second topdress during spring based on the pre- distinct row arrangement; row intercrop- crop either provides a reduced area for cipitation outlook. However, actual yield ping, at least one crop is planted in rows; weeds to get a foothold or reduces weed depends on the amount of precipitation in strip intercropping, growing crops in strips through competition or allelopa- that season. If all the fertilizer is applied at wide enough to separate them, yet nar- thy. One study showed that intercropping planting and if precipitation turns out to row enough to allow interaction between corn (Zea mays L.) and sorghum (Sorghum be below average or even under them; and relay intercropping, growing bicolor [L.] Moench) with desmodium conditions, the crop has been over fertil- two or more crops during differing parts (Desmodium spp.), effectively controlled ized, and it uses up all available water, and of their life cycles. Whenever two crops are witchweed (Striga hermonthica Del.) (Khan dries out. Using intercropping, N-smart planted together they will interact either or et al. 2007); another showed that a cover cropping systems could be developed. The both in competition (for light, water, and crop of velvetbean (Mucuna deeringiana alternative for these farmers would be to nutrients) and facilitation (Vandermeer [Bort] Merr.) reduced weed biomass by a legume and wheat in the same field. 1992). That is, they may have negative and 68% in corn (Caamal-Maldonado et al. The legume can then be killed at appropri- positive effects on each other. Of course, 2001). ate times to avoid too much competition intercropping works best when the posi- If intercropping is, indeed, experienc- with the primary crop. The goal would be tive effects are stronger than the negative ing a renaissance in response to problems to apply starter N to get the crops going ones. Intercropping success depends on a with monoculture, this should not be seen and then rely on the legume to make the good balance between competition and as going back to ancient peasant ways, but, “decisions” whether or not to add N to facilitation. Examples of strong facilita- rather, as adopting useful aspects of the the system; the “decisions” would be based tion include triticale (Triticosecale) that practice to modern agriculture. However, on available soil moisture. The process of provides a strong stem for the vetch ( the methods described above will likely N fixation is energy consuming, and the spp.) , while vetch provides the nitro- find their best use in modern organic - legume will use the easily available N if gen for the triticale (Vandermeer 1992). ing. In fact, is a perfect fit too much is applied at planting, so the A second crop, whether serving as a cover for intercropping as fossil--based inputs proposed system will not . Similarly crop or a windbreaker may increase soil and synthetic pesticides are not allowed. N fixation is sensitive to stress, and when water retention. A windbreaker alters Intercropping can also fit into conven- the legume senses drought the plant will the microclimate of the sheltered crop, tional cropping systems. Intercropping stop fixing N (Sinclair et al. 1987), thereby which could be very useful in the Pacific provides increased diversity, which facili- overfertilization is avoided. On the other Northwest, where gusty wind following tates better biological control of pests hand, if environmental conditions permit, rain would ordinarily evaporate the sparse and reduced soil . inter- the legume can add as much N as possible water received. But, on the other hand, the cropped with can provide not only to the system, presumably leading to high windbreaker crop may also compete with nitrogen, but also other minerals, soil cover, yields of the primary crop. The Columbia the sheltered crop for the water. as they also smother weeds, provide Basin Agricultural Research Center’s field One important reason intercrop- for pest predators, and increase micro- trials that began in 2003 show that in a ping is popular in the developing world bial diversity, such as vesicular arbuscular 279 mm (11 in) precipitation zone (Moro, is that it is more stable than monocrop- mycorrhizae (VAM). VAM, a , plays Oregon), yields of wheat intercropped ping (Horwith 1985). In Africa and South an interesting role in that it is thought to with winter pea (seeded at a reduced rate) Asia, where environmental stress is com- facilitate nutrient transfer—e.g., phospho- were 12% to 14% higher than the pure mon, intercropping is an against rus—to the other crop. The association wheat control plot; in the 406 mm (16 in) total crop failure (Horwith 1985). The with VAM becomes very significant where precipitation zone (Pendleton, Oregon), stability under intercropping is attrib- one crop has the ability to mine different yield was 4% to 9% higher. uted to the partial restoration of diversity sources of nutrients than the other. Some But before intercropping can be widely lost under . The most well evidence shows more P, K, Ca, and Mg adopted by organic and conventional documented advantage of intercropping availability in intercrops than in monocul- farmers, considerably more research is is reduced damage from insects, nema- tures (Vandermeer 1992; Li et al. 2007). needed. Choosing and managing inter- todes, and disease. One crop may serve as a Intercropping might also be able to crops requires good planning, that includes deterrent (disruptive mechanism) whereby solve the nitrogen dilemma for winter selection of appropriate , proper

PROOF * NOT FOR DISTRIBUTION 56A March/April 2009—vol. 64, no. 2 journal of soil and water conservation spacing, etc. For example, in the trials systems, it seems reasonable to continue Horwith, B. 1985. A role for intercropping in modern mentioned above, the docile pea variety research on the possibilities of growing agriculture. Biological Sciences 35(5):286-291. chosen worked well with the wheat, but more than one crop in a field at the same Huang, Wen-yuan. 2007. Impact of Rising Natural when a different pea had to be selected, it time. Gas Prices on U.S. Ammonia Supply. Outlook turned out to be far too aggressive, out- Report No. (WRS-0702). , DC: competing the wheat. Choices of plants References USDA Economic Research Service. for intercrop farming and for research Andersen, M.K. 2005. Competition and comple- Kass, D.C.L. 1978. cropping systems: trials are, of necessity, limited to selec- mentarity in annual intercrops—the role of review and analysis. Cornell International tions that have been bred for monoculture plant available nutrients. PhD thesis, Department Agricultural Bulletin 32. systems. The time when plant of Soil Science, Royal Veterinary and Khan, Z.R., C.A.O. Midega, A. Hassnalli, J.A. Pickett, have intercropping in mind is far into the Agricultural University, Copenhagen, . and L.J. Wadhams. 2007. Assessment of different future. If and when an effective intercrop- Samfundslitteraur Grafik, Frederiksberg, legumes for control of striga hermonthica in ping breeding program is established, it Copenhagen. maize and sorghum. Crop Science 47:730-736. would require understanding all the com- Brenner, L. 1991. Dollars and sense: The economic Li, L., S.-M. Li, J.-H. Sun, L.-L. Zhou, X.-G. Bao, petitive and facilitative principles involved benefits of reducing pesticide use. Journal of H.-G. Zhang, and F.-S. Zhang. 2007. Diverstiy in crops working well together. Similarly, Pesticide Reform 11(2):18-20. enhances agricultural productivity via rhizosphere most intercropping studies in the past have Caamal-Maldonado, J.A., J.J. Jiménez-Osornio, A. phosphorus facilitation on phosphorous-deficient focused on yields, with little emphasis on Torres-Barragán, and A.L. Anaya. 2001. The use . Proceedings of the National Academy of the basic inter-specific processes that con- of alleopahic legume cover and species Sciences 104:11192-11196. tribute to those yield results. The success for in cropping systems. Sinclair, T. R., R. C. Muchow, J. M. Bennett and L. C. of an intercrop system depends on under- Journal 93:27-36. Hammond. 1987. Relative sensitivity of nitrogen standing the physiology of the species to Food and Agricultural Organization. 2008. Current and biomass accumulation to drought in field- be grown together, their growth habits, World Fertilizer Trends and Outlook to 2011/12. grown soybean. Agronomy Journal 79:986-991. canopy and architecture, and water Rome: Food and Agriculture Organization, Sullivan, P. 2003. Intercropping principles and pro- and nutrient use. Plants compete for light United Nations. duction practices. Appropriate above ground and for water and nutrients Horrigan, L., R.S. Lawrence, and P. Walker. 2002. Transfer for Rural Areas Publication. http:// below grown, so competition involves a How ES can address www.attra.ncat.org. combination of light and soil factors in the environmental and health harms of Vandermeer, J. 1992. The of intercropping. space and time. What begins as a nutrient . New York, NY: Cambridge University Press. competition may end up as a shade issue, Perspectives. 110:445-456. as different species compete for various resources at differing times in their growth cycle. This complexity may be discourag- ing research in these areas (Vandermeer Successful Seedings Include 1992). The biggest obstacle in adopting inter- Truax Equipment cropping systems is to conceptualize the planting, cultivation, fertilization, spraying, and, particularly, harvesting of more than one crop in the same field. Agronomic recommendations simply do not exist. Furthermore, given the numerous inter- crop combinations possible and the myriad of climatic and soil conditions involved, Our Secret generalization to recommendations may • Precision Seed Placement & Seed-to- • Flexible planter assemblies that not be possible. Once the potential ben- Soil Contact Hug the Ground efits of intercropping are realized, and the • Seed small legumes, fluffy grasses & • Plant in heavy sod, crop will develops, mechanization could be in one operation residue, or a prepared seedbed developed for these potentially benefi- cial systems, but it will take a long time before mechanized intercropping systems call: 763-537-6639 will rival the current monoculture systems. Truax Company web: www.truaxcomp.com Given the advantages to be enjoyed from 4300 Quebec Avenue North e-mail: [email protected] intercropping and the environmental and New Hope,MN 55428 economic problems with current farming

PROOF * NOT FOR DISTRIBUTION journal of soil and water conservation March/April 2009—vol. 64, no. 2 57A